Circuit breakers when mounted through a panel on a surface usually have their terminals on different sides of the circuit breaker assembly. The manual reset circuit breakers are generally constructed so that it is not readily seen that the circuit breaker has opened to protect the circuit from an overload or a surge in current.
Both the manual and the auto reset high amp circuit breaker assemblies which are generally available are relatively difficult to manufacture. The bimetallic bistable elements used to open and close the breaker circuit usually require a relatively complex structure to operate with the quickness that is necessary to protect a circuit from damage. The structure used is a cylindrical bimetallic disc that has a small clearance hole at the center. The disc is then stamped into a dome shaped element via a radial forming die. A finely threaded screw is placed through the center hole and engaged into a mating female thread within the units main housing. The screw is tightened to preload the central dome or hump. The disc has a pair of contacts on opposite sides of the diameter. In the assembly the disc contacts have corresponding contacts attached to termination lugs. When the disc circuit breaker encounters an over-current, the disc goes from concave to convex to open the circuit and returns in the automatic reset style when the over-current is not present and a predetermined time has past to allow the element to sufficiently cool. The manual reset style operates similarly except that the bistable element is over-stressed so that when an over-current causes the convex condition, the element must be returned to the concave form by physical force via a push-button resetting mechanism.
These types of circuit breakers for low voltage DC applications with high amperage rating utilize generally large and broad forming radii that as a process exhibits high variability. This results in circuit breakers which are relatively costly to manufacture because the manufacturing process is labor intensive. Each unit has to be individually calibrated at the factory. The center adjusting screw for each unit must be manually tightened to bring the contacts into a pre-load condition. Then each unit must be tested to be sure it is properly calibrated to open and close as required to protect a circuit.
Present circuit breakers do not provide a means for manually placing the circuit breaker in an open circuit condition, thus the time consuming and difficult step of disconnecting the batteries is often necessary.
Some existing circuit breakers provide a means to work on electrical equipment without disconnecting a battery terminal or otherwise removing the electrical source from the circuit; however, they are relatively expensive, complex, and not available or suitable in this class of low voltage, high current D.C. design.